"The Atlas moth is a monstrous thing! Not only is it one of the largest moths in the world...The tips of its wings look rather like the heads of venomous snakes! Despite its largeness and loathsome looks, the adult Atlas moth lives only for a few days. It emerges from its cocoon without a mouth, you see...and so cannot eat. I feel for the poor thing... but it is still foul!"

The Atlas moth is one of the largest lepidopterans with a wingspan measuring up to 24 cm (9.4 in) and a wing surface area of about 160 cm2 (~25 in2). It is only surpassed in wingspan by the white witch (Thysania agrippina) and in wing surface area by the Hercules moth (Coscinocera hercules). As in most Lepidoptera, females are noticeably larger and heavier than males, while males have broader antennae.

The body is disproportionately small compared to the wings. The upperside of the wings are reddish brown with a pattern of black, white, pink, and purple lines and triangular, scale-less windows bordered in black. The undersides of the wings are paler. Both forewings have a prominent extension at the top.

The Atlas moth has no mouth; every flight takes valuable energy and can take days off their already short lives, as it has a very short life span of only one to two weeks. They conserve energy by flying as little as possible. A female will wait for a male to come along and be fertilised, lay eggs and die.

Atlas moths are a saturniid moth, a group that includes the famous luna moth. Despite what their common name suggests, they are only distant cousins of the domestic silk moth (Bombyx mori) which belong to the family Bombycidae.